1. Field of the Invention
The present invention relates to the fields of laser, integrated circuit, networking, and data communication. More specifically, the present invention relates to laser driving techniques having particular applications for data communication and networking.
2. Background Information
With advances in integrated circuit, microprocessor, networking and communication technologies, an increasing number of devices, in particular, digital computing devices, are being networked together.
Examples of computing devices include servers, personal computers and “special” purpose computing devices. Personal computers may have form factors, such as desktop, laptop, tablet, and so forth. “Special” purpose computing devices may include personal digital assistants (PDA), wireless mobile phones and so forth.
The various computing devices are often first coupled to a wired or wireless local area network (LAN), such as an Ethernet based office/home network. In turn, the local area networks are interconnected together through wired or wireless wide area networks (WAN), such as SONET networks, ATM networks, Frame Relays, and the like. Of particular importance is the TCP/IP based global inter-network, the Internet.
As a result of this trend of increased connectivity, an increasing number of applications that are network dependent are being deployed. Examples of these network dependent applications include but are not limited to, the world wide web (WWW), email, Internet based telephony, and various types of e-commerce and enterprise applications.
The success of many content/service providers as well as commerce sites depend on high speed delivery of a large volume of data across wide areas. As a result, high speed data trafficking devices, such as high speed optical, or optical-electro routers, switches and so forth, (hereinafter collectively referred to as optical networking devices), are needed.
Many optical networking devices are laser based, include networking interfaces with components to output lights encoded with the data to be communicated between the devices. Often, a laser diode is employed to output light, and a laser driver is employed to drive the laser diode.
FIG. 8 illustrates a typical drive pulse employed by a laser driver to drive a laser diode under the prior art, and the resulting light power outputted by the laser diode. Drive pulse 800 is a simple waveform including a rising portion 802 where drive pulse 800 rises from an initial current level to a peak current level at a very fast transition rate, taking a very small fraction of a nanosecond, a steady portion 804 where drive pulse 800 is sustained at the peak current level for a duration, and a falling portion 806 where drive pulse 800 falls/drops from the peak current level back to the initial current level at a very fast transition rate, taking also only a very small fraction of a nanosecond.
As illustrated, the laser output 850 typically has overshoot 862 as well as undershoot 864 before it can settle at a desired output level 854 or back at a “rest” level 852. Overshoot 862 and undershoot 864 are undesirable, as they impair the quality of laser output 850. However, under the prior art, the effects are believed to be unavoidable, and the phenomenon is referred to as the relaxation oscillation effect.
Thus, it will be desirable to tame the relaxation oscillation effect when driving a laser, i.e. reduce the amount of overshoot and/or undershoot.